Your issue is the formatting of the data in the file. 4650 is in the csv as "4,650" which Tableau (or rather JET, the MS product that Tableau uses as the interface) reads that as the text 4,650. Unfortunately JET has also already made the decision that the column is a number, so then discards the text resulting in NULL.
You have a number of options.
- Take the data through Excel, save as an Excel file and connect Tab to this
- Change the output of your data to output proper numbers not with commas
- Write a schema.ini (http://msdn.microsoft.com/en-us/library/ms709353%28VS.85%29.aspx) to force JET to consider this column as text, then deal with the commas in Tableau.
Even though JET is causing this I regard this as a Tableau error - Tableau should warn you about the high number of nulls.
Alex, thank you for taking the time and detailing the suggestions. I will save these files without the comma separators.
Many thanks again for your help.